Ancient bacteria could improve anti-ageing cosmetics

Where better to look for a sunscreen formula than in cyanobacteria – organisms that thrived on Earth before there was enough oxygen to block harmful ultraviolet light? The genes and enzymes responsible for producing sunscreen molecules in one such cyanobacterium have now been identified, a step towards making bio-inspired sun protection.

Also known as blue-green algae, cyanobacteria have existed on Earth for 3.4 billion years. They get their energy from sunlight via photosynthesis, but in doing so, they must expose themselves to UV radiation, which damages DNA molecules – a serious problem for early life, before the "great oxygenation event" around 2.4 billion years ago. One way today's cyanobacteria combat UV exposure is to make small-molecule sunscreens called mycosporines and mycosporine-like amino acids (MAAs) that absorb the harmful rays.

Previous studies have focused on the chemical structures of these UV-blocking molecules and the kinds of organisms that make or accumulate them in different habitats. No one knew how the organisms make the molecules, however.

Now Emily Balskus and Christopher Walsh of Harvard Medical School in Boston, Massachusetts, have found the genes and enzymes involved in the biosynthesis of these sunscreen molecules for the first time.
Genome mining

Using a genome-mining approach, the duo identified a gene cluster that could be responsible for making sunscreen molecules in a cyanobacterium called Anabaena variabilis. To test the genes, they expressed the cluster in the bacterium Escherichia coli, which normally does not make sunscreen molecules. Afterwards, the team found the bacteria could make the molecules.

The pair then found that four enzymes were responsible for synthesising the MAA molecules. Each MAA has two amino acids linked to a central organic group. It's the amino-acid linkages that are important for determining the wavelength and strength of UV absorbance, they say.

The MAAs shinorine and porphyra-334 have already been used in an "anti-ageing" cosmetic product, Helioguard 365, manufactured by Mibelle Biochemistry, a company based in Buchs, Switzerland. However, Mibelle extracts these chemicals directly from algae. "Our work could be a starting point for devising new routes to these molecules or analogues using a biocatalytic or biological engineering approach," says Balskus.